Project Summary Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy, with a median 5-year survival of around 7%. The poor prognosis of PDAC patients is due to a combination of factors, including late stage diag- nosis, low drug accumulation due to poorly perfused tumors, and an immunosuppressed tumor microenviron- ment. Consequently, while significant progress has been made in immunotherapy against other cancer types such as melanoma and non-small cell lung cancers, clinical trials of immunotherapy for PDAC have not yet proven to be successful. One avenue of investigation for reversing local immunosuppression has been the inhi- bition of chemokine receptor CXCR4 in combination with chemotherapeutic and ?PD-1 compounds. CXCR4 serves as a receptor for CXCL12, which is secreted by cancer associated fibroblasts and regulates T-cell influx into tumors. Recently, it has been discovered the CXCR7 also serves as a receptor for CXCL12, in addition to several other chemokines. Given its elevated expression in PDAC stroma, we hypothesized that CXCR7 may serve as a candidate therapeutic target for reversing PDAC immunosuppression. Recent advances in synthetic biology have stimulated interest in programming bacteria to sense and respond to diseases in the human body such as cancer. Bacterial machinery can be re-engineered to sense a particular microenvironment, initiate colonization, and trigger the production of a therapeutic directly and specifically within that microenvironment. Particularly relevant for PDAC, the ability of bacteria to move through tissues without a robust, direct vasculature connection offers a great advantage for drug delivery to poorly perfused tumors. Leveraging our expertise in synthetic biology, molecular biology, mouse models, and preclinical therapeutics, we will interrogate the role of CXCR7 in the maintenance of local immune suppression in PDAC and evaluate the preclinical efficacy of targeting this pathway as a means of therapeutic intervention in PDAC. First, we will examine the functional consequences inhibiting CXCR7 and its pathway components in the multiple cell types in PDAC and elucidate the molecular mechanism of immune suppression via scRNAseq analysis and multiplex immunofluorescence of PDAC explants. To study the effects of CXCR7 inhibition in vivo, we will administer probiotic E. coli Nissle 1917 engineered to selectively colonize tumors and produce CXCR7 inhibiting nanobodies directly within the tumor of our preclinical model of PDAC, the KPC mouse. Tumor progression, immune system activation, and overall survival will be assessed following CXCR7 monotherapy and in combination with tradi- tional chemotherapeutics and other immune-targeted agents. In summary, the experiments proposed herein will aid our understanding of the local immune suppression within PDAC tumors as well as validate a bacterial therapy that addresses two challenges of PDAC treatment; poor drug accessibility and a highly suppressed immune microenvironment.